Scapula forms an important component of the shoulder girdle. The
triangular shape of the scapula is a characteristic feature of mammals
and is not due to forces applied during development. Scapular shape has
undergone modifications which can be expressed as scapular index
indicating relationship of length to breadth of the bone. Shape change
is mostly in the infraspinatus portion.

Acromion process of scapula has been classified by many researchers
into three types. Type 1 flat; type 2 curved; type 3 hooked. Variations
of acromion has been associated with sub acromial impingement syndrome
and rotator cuff tear. Glenoid cavity is considered as the head of the
scapula. Different shapes of the glenoid cavity have been described;
pear shaped, round, oval or inverted comma shaped. Variations in shape
is important clinically, especially for shoulder arthroplasty.
Variations in suprascapular notch with or without an anomalous superior
transverse scapular ligament is a cause for suprascapular nerve
entrapment syndrome.

Determination of sex using scapular measurements is very useful in
medicolegal cases, natural disasters and in circumstances where other
bones are fragmented or not available.

Scapular measurements can be used for comparative anatomy, for
surgical procedures and for manufacturing prosthetics. The dimensions of
scapula are important in the case of rotator cuff diseases, shoulder
arthroplasty and in recurrent shoulder dislocation.

MATERIALS AND METHODS

Fifty adult dry human scapulae were included in the study of which
25 were of the left side and 25 of the right. The study was conducted in
Government T D Medical college Alappuzha, Kerala.

Study Design

Descriptive study.

The Parameters Related to Scapula as a whole, Acromion Process and
Glenoid Cavity were Measured using Vernier Callipers. They were

* Length of scapula in mm is taken as the distance between the
summit of the superior angle and the inferior angle.

* Scapular breadth is the distance between the spine intersecting
the medial border of scapula and the middle of outer border of glenoid
cavity.

* Infraspinatus length is the distance between the point of
intersection of spine of scapula to medial border and tip of inferior
angle.

* Scapular index and infraspinatus index were measured using the
above readings as follows.

Scapular index = breadth/length x 100.

Infraspinatus index = breadth/infraspinatus length x 100.

* Length of acromion process in mm is the distance between the tip
and the posterior border of acromion process.

* Breadth of acromion process is the distance between the medial
and lateral borders at the midpoint of acromion process.

* Thickness of acromion process was measured at the anterior part.

* The acromiocoracoid distance is the distance between the tip of
acromion process and tip of coracoid process (fig. 7C).

* The acromioglenoid distance is the space between tip of acromion
process and the supraglenoid tubercle (fig. 7B).

* Length of glenoid cavity (superior-inferior glenoid diameter):
maximum distance between most inferior point on glenoid margin to
supraglenoid tubercle.

All measurements of left and right scapulae were made and
tabulated. Mean and standard deviation were calculated manually.

In order to test whether the various parameters of left and right
scapulae were different significantly, the equality of measure was
tested using a small sample test, student 't test, for unpaired
independent samples. Values of t was computed using an online
calculator, the URL of which is www.socscistatistics.com/

Figures Showing Measurements of Scapula

RESULTS

The total length of scapula in the present study ranged from 110.3
mm to 148.3 mm on the left side and 105 to 149.9 mm on the right (table
1) with mean value of 130.8 & 130.11 and standard deviation of 11.05
& 10.96 respectively, which was statistically insignificant (t =
0.7, p = 0.4)

Increased breadth was seen on right scapulae compared to those on
the left as shown in table 2 but was insignificant statistically (t =
0.45, p = 0.32).

Correlation between breadth and infraspinatus length of scapula
(infraspinatus index) was in the range of 81.3 -103.6 on the left and
82.1 - 105 on the right (table 5) and was not significant statistically
(t = -0.643, p value = 0.26).

Broader acromion processes were seen on right scapulae with mean
value of 24.86 on the left and 27.36 on the right side and is
statistically significant (t = -2.763, p value = 0.004) p<0.05 as
seen in table 7.

Thickness of acromion process was higher on the right scapulae with
mean values of 6.52 and SD 1.22 on left and 7.52 and SD 1.77 on right
(table 8) which is significant statistically. (t = -2.15, p value =
0.017).

Acromiocoracoid distance was not significantly different on both
scapulae (t = 0.31, p = 0.37) as shown in table 9.

Acromioglenoid distance of both sides did not differ significantly
(table 10).

Table 11 shows statistically significant increase of glenoid cavity
length on right scapulae with mean value of 34.92 and SD 2.14 on the
left and mean value 36.92 and SD 1.81 on the right.

Type II suprascapular notches were more commonly seen on left
scapulae whereas Types II & III were equally seen and more common on
right scapulae (Table 16 & Chart 3).

DISCUSSION

Since the scapula varies in morphology, its measurements have
importance in shoulder girdle pathologies. Each individual presents with
variations in shoulder anatomy, overall conditioning and fitness and
degrees of shoulder laxity that makes the precise evaluation of
pathologic lesions difficult. [1] The slope and length of the acromion
and the height of the arch are most closely associated with degenerative
changes. [2]

Scapular Length

Mean scapular length was 132.38 mm with standard deviation of 11.05
on left scapulae and 130.11 mm with SD of 10.96 on right scapulae in our
study. Gupta [3] et al reported mean scapular length of 135.3 mm with SD
of 10.9 which is similar to our study. Maximum scapular height is the
maximum distance between the highest point of the superior angle and the
lowest point of the inferior angle. [4]

Scapular Breadth

Maximum scapular breadth is the maximum distance between the point
on the longitudinal axis of the glenoid cavity and the point on the
prolongation of the inferior boundary of the closed margin of the spine.
The mean breadth of scapula was 89.68 mm with SD of 8.88 on left
scapulae and 90.9 mm with SD of 6.20 in the present study which was in
accordance with Gupta et al.

Infraspinatus Length

The change in shape of scapula is more common in infraspinatus
region. The mean infraspinatus length was 98.54 mm with SD of 10.41 on
left scapulae and 99.32 mm with SD of 8.02 on the right, while
Krishnaiah [5] et al reported a higher value of 107.71 mm with SD of
7.6.

Scapular Index

Scapular indices help in determining the race. The mean scapular
index observed in our study was 67.72 with SD of 3.72 on the left and
70.01 with SD of 4.09 on the right scapulae which is less than those of
Krishnaiah's study which showed 73.99 with SD of 4.6.

Infraspinatus Index

The present study showed a mean infraspinatus index of 90.93 with
SD of 4.96 on left and 91.90 with SD of 5.48 on right scapulae.

Length of Acromion Process

Acromion process plays a significant role in formation and
stability of shoulder joint. Our study showed a mean acromial length of
42 mm with SD of 5.23 on left and 42.11 mm with SD of 4.14 on right
scapulae whereas Mansur [6] et al found mean length of 45.57 mm with SD
of 5.1 on left and 46.46 mm with SD of 5 on right acromion in Nepalese
population.

Breadth of Acromion

The mean breadth of acromion in our scapulae were 24.86 mm with SD
of 2.88 on the left and 27.36 mm with SD of 3.81 on right acromial
processes, while Mansur et al found mean breadth of 27.23 mm with SD of
3.06 on left and 26.63 mm with SD of 3.55 on the right acromion
processes, which is in accordance to our study.

Acromial Thickness

Acromial thickness showed a mean value of 6.52 mm with SD of 1.22
on the left and 7.52 mm with SD of 1.77 on the right indicating an
increase on the right acromia.

Shape of Acromion

44% of scapulae on left revealed tubular acromion processes whereas
56% were rectangular on the right. The second commonest was rectangular
(40%) on left and tubular (28%) on the right. Acromion process was
classified into three types on the basis of its shape into triangular,
quadrangular, and tubular by Mansur et al. Curved acromia were also
seen. The under surface of anterior one third of acromion was pointed
out by Neer [7] as the area responsible for impinging upon the
components of the rotator cuff especially the supraspinatus tendon.
Rotator cuff lesions are common where subacromial space is narrow.

Acromiocoracoid Distance and Acromioglenoid Distance

No significant difference of these were noted between scapulae of
both sides in the present study.

Glenoid Cavity Length

Height of the glenoid cavity is the maximum distance from inferior
point of glenoid margin to the most prominent point on supraglenoid
tubercle. Mean value of 34.92 mm with SD of 2.14 was noted on the left
and 36.92 mm with SD of 1.81 on the right glenoids and the difference
was highly significant and was similar to the study by Patil et al. The
left glenoid cavities were slightly shorter in length in comparison to
the right.

Glenoid Cavity Breadth 1

Glenoid cavity breadth is the maximum breadth of the articular
margin, perpendicular to glenoid cavity height. The mean of maximum
diameter of lower part of glenoid cavity was 22.19 mm with SD of 1.52 on
the left and 23.91 mm with SD of 2.91 on the right.

Glenoid Cavity Breadth 2

The mean of diameter of upper part of glenoid cavity was 16.27 mm
with SD of 2.51 on left and 16.52 with SD of 2.48 on the right glenoids
and was in accordance with Patil [8] et al. But Iannoti [9] et al found
a mean diameter of 23 mm with SD of 2.7 which is higher than that of our
study.

Shape of Glenoid Cavity

The glenoid cavity has been classified into pear shaped, inverted
comma or oval, based on the presence of a notch on the anterior glenoid
rim, [10] Pear-shaped glenoids were more frequently seen on left
scapulae (52%) and inverted comma shaped ones (40%) on the right.

Suprascapular Notch

Suprascapular notch is a depression on the lateral part of superior
border of scapula, medial to the coracoid process. It is bridged by
superior transverse scapular ligament which may ossify and the foramen
then transmits suprascapular nerve to supraspinatus fossa. [11,12] Bony
foramina were seen in 12% of left scapulae while none was found on the
right. This notch is an important landmark of suprascapular nerve during
arthroscopic shoulder surgery. [13,14] Rengachary's [15]
classification of suprascapular notches says that in type 1, the
superior border of scapula present a depression from the medial superior
angle to the base of coracoid process; type II is described as a wide
blunted V shaped notch, occupying nearly a third of the superior border
with the widest point along the superior border. Type III is a symmetric
and "U" shaped notch while type IV is described as a very
small "V" shaped notch frequently presenting a shallow groove
near the notch; type V is similar to type III with partial ossification
of medial border of the notch and with minimum diameter along superior
border of scapula. Type VI is described as a bony foramen with a
completely ossified superior transverse scapular ligament. In the
present study, suprascapular notches were classified by Polguj's
[16] classification and type II was more common (36%) on left scapulae
than that on right (32%) whereas type III showed equal distribution (32%
each) on both sides. Suprascapular notch was absent in 12% on the left
and 16% on the right.

In the whole population, approximately 1-2% of all shoulder pain is
caused by suprascapular nerve impingement syndrome. [17] According to
Albino, [18] suprascapular entrapment syndrome is more likely to be
associated with type III notch because of its peculiar features.

CONCLUSION

Scapular index indicates the relationship of breadth to length of
scapula and reveals modifications in shape of the bone and is useful to
compare racial differences. Right scapulae of the study group showed
higher indices than left scapulae.

Acromion thickness and acromial breadth were slightly more in
right-sided scapulae. The different shapes and curvature of acromion has
a role in impingement syndrome.

Glenoid cavity was longer on right scapulae in the present study
and may be of significance to surgeons in shoulder arthroplasty.